Semiconductor devices, such as memory devices and processors, transmit data across data communication lines that are configured to have carefully matched impedance values. Variations in certain operating parameters such as temperature or the like can result in impedance mismatches that can adversely affect data transmission rates and quality. In order to mitigate these adverse scenarios, memory devices may include programmable impedance termination components that have impedance values that can be adjusted as operating conditions change. In some implementations, programmable impedance termination components are calibrated based on voltage measurements made on a circuit node that connects to an external resistor. In some cases, a limited number of external connections are available for connection to an external resistor. These external connections may be shared between multiple devices that use the connection for calibration purposes. Thus, contention for use of the external connection may arise when two or more devices attempt to use the external connection at the same time or substantially the same time.